Mojo: Armed Watchers

mojo/public/cpp/bindings/lib/connector.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/public/cpp/bindings/connector.h"
 
 #include <stdint.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 170 matching lines @@
   return sync_watcher_->SyncWatch(should_stop);
 }
 
 void Connector::SetWatcherHeapProfilerTag(const char* tag) {
   heap_profiler_tag_ = tag;
   if (handle_watcher_) {
     handle_watcher_->set_heap_profiler_tag(tag);
   }
 }
 
+void Connector::EnableNestedDispatch(bool enabled) {
+  nested_dispatch_enabled_ = enabled;
+  handle_watcher_.reset();
+  WaitToReadMore();
+}
+
 void Connector::OnWatcherHandleReady(MojoResult result) {
   OnHandleReadyInternal(result);
 }
 
 void Connector::OnSyncHandleWatcherHandleReady(MojoResult result) {
   base::WeakPtr<Connector> weak_self(weak_self_);
 
   sync_handle_watcher_callback_count_++;
   OnHandleReadyInternal(result);
   // At this point, this object might have been deleted.
   if (weak_self) {
     DCHECK_LT(0u, sync_handle_watcher_callback_count_);
     sync_handle_watcher_callback_count_--;
   }
 }
 
 void Connector::OnHandleReadyInternal(MojoResult result) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
   if (result != MOJO_RESULT_OK) {
     HandleError(result != MOJO_RESULT_FAILED_PRECONDITION, false);
     return;
   }
+
   ReadAllAvailableMessages();
   // At this point, this object might have been deleted. Return.
 }
 
 void Connector::WaitToReadMore() {
   CHECK(!paused_);
   DCHECK(!handle_watcher_);
 
-  handle_watcher_.reset(new Watcher(FROM_HERE, task_runner_));
+  handle_watcher_.reset(new SimpleWatcher(
+      FROM_HERE, SimpleWatcher::ArmingPolicy::MANUAL, task_runner_));
   if (heap_profiler_tag_)
     handle_watcher_->set_heap_profiler_tag(heap_profiler_tag_);
-  MojoResult rv = handle_watcher_->Start(
+  MojoResult rv = handle_watcher_->Watch(
       message_pipe_.get(), MOJO_HANDLE_SIGNAL_READABLE,
       base::Bind(&Connector::OnWatcherHandleReady, base::Unretained(this)));
 
   if (rv != MOJO_RESULT_OK) {
     // If the watch failed because the handle is invalid or its conditions can
     // no longer be met, we signal the error asynchronously to avoid reentry.
     task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&Connector::OnWatcherHandleReady, weak_self_, rv));
+  } else {
+    handle_watcher_->ArmOrNotify();
   }
 
   if (allow_woken_up_by_others_) {
     EnsureSyncWatcherExists();
     sync_watcher_->AllowWokenUpBySyncWatchOnSameThread();
   }
 }
 
 bool Connector::ReadSingleMessage(MojoResult* read_result) {
   CHECK(!paused_);
 
   bool receiver_result = false;
 
   // Detect if |this| was destroyed or the message pipe was closed/transferred
   // during message dispatch.
   base::WeakPtr<Connector> weak_self = weak_self_;
 
   Message message;
   const MojoResult rv = ReadMessage(message_pipe_.get(), &message);
   *read_result = rv;
 
+  if (nested_dispatch_enabled_) {
+    // When supporting nested dispatch, we have to rearm the Watcher immediately
+    // after reading each message (i.e. before dispatch) to ensure that the next
+    // inbound message can trigger OnHandleReady on the nested loop.
+    handle_watcher_->ArmOrNotify();
+  }
+
   if (rv == MOJO_RESULT_OK) {
     receiver_result =
         incoming_receiver_ && incoming_receiver_->Accept(&message);
   }
 
   if (!weak_self)
     return false;
 
   if (rv == MOJO_RESULT_SHOULD_WAIT)
     return true;
 
   if (rv != MOJO_RESULT_OK) {
     HandleError(rv != MOJO_RESULT_FAILED_PRECONDITION, false);
     return false;
   }
 
   if (enforce_errors_from_incoming_receiver_ && !receiver_result) {
     HandleError(true, false);
     return false;
   }
   return true;
 }
 
 void Connector::ReadAllAvailableMessages() {
   while (!error_) {
+    base::WeakPtr<Connector> weak_self = weak_self_;
     MojoResult rv;
 
-    if (!ReadSingleMessage(&rv)) {
-      // Return immediately without touching any members. |this| may have been
-      // destroyed.
-      return;
-    }
-
-    if (paused_)
+    // May delete |this.|
+    if (!ReadSingleMessage(&rv))
       return;
 
-    if (rv == MOJO_RESULT_SHOULD_WAIT)
-      break;
+    if (!weak_self || paused_)
+      return;
+
+    DCHECK(rv == MOJO_RESULT_OK || rv == MOJO_RESULT_SHOULD_WAIT);
+
+    if (rv == MOJO_RESULT_SHOULD_WAIT) {
+      // Attempt to re-arm the Watcher.
+      MojoResult ready_result;
+      MojoResult rv = handle_watcher_->Arm(&ready_result);

[yzshen1, 2017/03/11 00:44:58]

Please consider using a different name, it hides |rv| of the outer scope.

[Ken Rockot(use gerrit already), 2017/03/12 22:24:13]

Done

+      if (rv == MOJO_RESULT_OK)
+        return;
+
+      // The watcher is already ready to notify again.
+      DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, rv);
+
+      if (ready_result == MOJO_RESULT_FAILED_PRECONDITION) {
+        HandleError(false, false);
+        return;
+      }
+
+      // There's more to read now, so we'll just keep looping.
+      DCHECK_EQ(MOJO_RESULT_OK, ready_result);
+    }
   }
 }
 
 void Connector::CancelWait() {
   handle_watcher_.reset();
   sync_watcher_.reset();
 }
 
 void Connector::HandleError(bool force_pipe_reset, bool force_async_handler) {
   if (error_ || !message_pipe_.is_valid())
@@ skipping 32 matching lines @@
 void Connector::EnsureSyncWatcherExists() {
   if (sync_watcher_)
     return;
   sync_watcher_.reset(new SyncHandleWatcher(
       message_pipe_.get(), MOJO_HANDLE_SIGNAL_READABLE,
       base::Bind(&Connector::OnSyncHandleWatcherHandleReady,
                  base::Unretained(this))));
 }
 
 }  // namespace mojo